REQUIRED PRACTICAL 2 : CULTURING MICROORGANISMS

Question 1

what is Bacterial culture is grown in?

Answer 1

a nutrient broth solution

Question 2

what does the nutrient broth contain?

Answer 2

it contains all the nutrients that bacteria need to grow and divide

Question 3

why is the broth cloudy?

Answer 3

it contains a very large number of bacteria

Question 4

what is another way to cultural bacteria?

Answer 4

another way to culture bacteria is to use an agar gel plate

Question 5

what do agar gel plates contain?

Answer 5

agar gel plates contain nutrient broth that’s been set into a jelly using a chemical called agar

Question 6

what then happens to agar gel plates after being set into a jelly using a chemical called agar?

Answer 6

this is then poured into a petri dish and allowed to set

Question 7

what do bacteria grow on an agar gel plate?

Answer 7

on an agar gel plate the bacteria grow divisible colonies

Question 8

label where these are on a diagram

• agar gel
• petri dish
• bacterial colonies

Answer 8

petri dish is the dish holding the agar gel and bacterial colonies

agar gel is found with the petri dish like jelly

bacterial colonies are found on the agar gel

Question 9

what can we do to to avoid contamination when making a nutrient broth solution? what does this do?

Answer 9

First, we sterilise all petri dishes, bacterial nutrient broth and agar.
This kills any unwanted microorganisms and prevents contamination

Question 10

why can our cultures be easily contaminated?

Answer 10

because there are lots of microorganisms such as bacteria and fungi naturally in the environment, these can very easily contaminate our cultures

Question 11

what is used to transfer bacteria into the culture.

Answer 11

an inoculating loop

Question 12

what must we do before we use the inoculating loop? how do we do this?

Answer 12

we must sterilise the inoculating loop before transferring bacteria into the culture. we do this by passing the inoculating loop through a bunsen burner flame.

Question 13

what do we do after transferring bacteria onto the dish?

Answer 13

next we attach the lid of the petri dish using adhesive tape. This stops the lid from falling off and unwanted microorganisms entering

Question 14

what do we do after placing the lid of the petri dish? explain why.

Answer 14

after placing the lid of the petri dish on, we then place the agar plate upside down into an incubator. This stops moisture from dripping down onto the bacteria and disrupting the colonies

Question 15

choosing the correct temperature:

in school labs, at what temperature do we normally incubate bacteria? Explain why we use this temperature.

Answer 15

25°C

Using this temperature, this reduces the chances that harmful bacteria will grow.

Question 16

REQUIRED PRACTICAL: effect of antibiotics on bacterial growth

Answer 16

1. Clean the bench with disinfectant solution. This kills microorganisms that could contaminate our culture.
2. sterilise an inoculating loop by passing it through a bunsen burner flame.
3. Open a sterile agar gel plate near a bunsen burner flame. The flame kills bacteria in the air
4. Now we use the inoculating loop to spread the chosen bacteria evenly over the plate
5. Place sterile filter paper discs containing antibiotic onto the plate
6. incubate the plate at 25°C

Question 17

After a few days, what results can we expect to see on our culture?

Answer 17

the bacteria forms a layer on the surface of the agar gel

around the antibiotic discs, we have a region where the bacteria have not grown. This is called the zone of inhibition

Question 18

how can we measure the effect of the antibiotic?

Answer 18

by calculating the area of the zone of inhibition, to do that we use this equation =
area =3.142r^2

Question 19

if radius is 12mm

calculate the area

Answer 19

area =3.142r^2
area =3.142 x12^2
area = 452.45mm^2